Fuel tanks on board vehicles of various kinds must generally meet sealing and permeability standards in relation to the type of usage for which they are designed and the environmental requirements with which they must comply. Both in Europe and throughout the world we are currently experiencing a considerable tightening of the requirements concerned with limiting the emissions of pollutants into the atmosphere and into the environment in general.
To limit these emissions, the Applicant has developed a method of molding a tank from a parison that includes at least one slot for introducing thereinto (and fastening thereto) (supports for) accessories during the actual molding of the tank and thus avoiding drilling openings (see for example Application EP 1 110 697).
The Applicant has also developed a particular method for this fastening (in situ snap-riveting, the subject of Application WO 2006/008308, the content of which is, for this purpose, incorporated by reference into the present application) and also an improvement of this method that is the subject of international Application EP 2008/059042 in the name of the Applicant, the content of which is also incorporated by reference into the present application.
The objective of this improvement is to provide an improved geometry of the snap-riveting zone that makes it possible to ensure self-centring of the accessory with respect to the tool which will carry out the snap-riveting and that makes it possible to obtain a better distribution of the stress during this process. This geometry consists of a concave relief at least partially surrounding the snap-riveting orifice and having a size and shape suitable for being able to cooperate with a protuberance (convex relief) of the tool during the snap-riveting.
The Applicant has successfully applied this improvement to the fastening of numerous accessories—or of the support thereof in the case of accessories that do not withstand the pressure and temperature conditions during molding—and/or for expensive accessories that should be dismantled from tanks that do not meet the standards before the latter are ground up (reduced to scrap that can be recycled during the molding of subsequent tanks).
In the particular case where the accessory is composed of the fuel pump (known as the “main feed pump” and supplying the engine of the vehicle with fuel), the support in question is in fact composed of what is referred to as the “swirl pot”. As its name indicates, the objective of this swirl pot is to constitute a fuel reserve for the cases where the vehicle negotiates a turn, drives on a slope, etc. or in any other situation where the pump suction point risks being exposed (no longer dipping in the fuel). One advantage of the process described above is that it makes it possible to provide a large capacity swirl pot, in particular when the parison is cut into two sheets. However, one drawback with which the Applicant has been confronted lies in the fact that as several types of pump exist, it is necessary to adapt the swirl pot depending on the pump chosen by the constructor and therefore, generally, to provide a swirl pot specific to each model, which is expensive (this part generally being based on a plastic molded in a mold specific to its (fixed) geometry).